Intra-amygdala microinjections of chlorpheniramine impair memory formation or memory retrieval in anxiety- and fear-mediated models

Abstract

H1 receptor histaminergic antagonist, chlorpheniramine (CPA) participates in cognitive performance in various animal models. However, little is known regarding the effects of CPA microinjection into the amygdala on emotional behavior. The purpose of this study was to investigate whether CPA microinjection into the amygdala has the same effect on two models, one anxiety- and the other fear-mediated, in various memory stages using the elevated plus maze (EPM) and the inhibitory avoidance task (IAT) tests. Two experiments were performed with seventy-two adult male Swiss mice. Behavioral testing was performed on two consecutive days, and in both experiments, before each trial, the animals received bilateral microinjections of saline (SAL) or CPA (0.16 nmol). The animals were re-exposed to the EPM or IAT 24h after the first trial. Four experimental groups were tested: SAL-SAL, SAL-CPA, CPA-SAL and CPA-CPA. In experiment 1, a decreased open arm exploration (% open arm entries, %OAE and% open arms time, %OAT) for SAL-SAL and SAL-CPA was showed, while these measures did not decrease for the CPA-SAL and CPA-CPA groups in Trial 2. In experiment 2, an increase of retention latency in relation to training 2 for the groups SAL-SAL and CPA-SAL and a significant decrease in latency for the group SAL-CPA was revealed. These results indicate that chlorpheniramine microinjection into the amygdala impairs emotional memory acquisition and/or consolidation in the EPM and retrieval of IAT.

Keywords: Amygdala; Elevated plus maze; Emotional memory; Inhibitory avoidance task.